add DiscoveryResponse info to SPs in discojson

[enriquepablo]

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This adds a discovery_responses key in the JSON produced by discojson for the SP entities that have DiscoveryResponse elements in their metadata.

This is to allow SeamlessAccess to warn users when they are sent to SeamlessAccess with a return URL that does not match the DiscoveryResponse elements published in the SP metadata.

[mikaelfrykholm]

@c00kiemon5ter I am taking a look at this. Setting up env. now.